Ionic liquid crystals.

Hybrid halide perovskites have become the “next big thing” in emerging semiconductor materials, as the past decade witnessed their successful application in high-performance photovoltaics. This resurgence has encompassed enormous and widespread development of the three-dimensional (3D) perovskites, spearheaded by CH3NH3PbI3. The next generation of halide perovskites, however, is characterized by reduced dimensionality perovskites, emphasizing the two-dimensional (2D) perovskite derivatives which expand the field into a more diverse subgroup of semiconducting hybrids that possesses even higher tunability and excellent photophysical properties. In this Perspective, we begin with a historical flashback to early reports before the “perovskite fever”, and we follow this original work to its fruition in the present day, where 2D halide perovskites are in the spotlight of current research, offering characteristics desirable in high-performance optoelectronics. We approach the evolution of 2D halide perovskites f...

Two-Dimensional Hybrid Halide Perovskites: Principles and Promises.

Synthesis, Structure, and Properties of Organic-Inorganic Perovskites and Related Materials

Organic–inorganic perovskites are a class of interesting compound in the perovskite family due to their unique structures of alternately stacking sheets of organic and inorganic components on the molecular scale. In this highlight, the basic knowledge and recent advances in organic–inorganic perovskites are reviewed with particular emphasis on the feature work including: the novel - and -oriented perovskite structures, synthesis, film preparation, patterning methods and optoelectronic properties of hybrid perovskites. Moreover, the small functional organic molecules can be templated into a regular arrangement by the inorganic perovskite framework. This unique material with nature-formed lamellar structure has the potential to be used as a template to create novel derivatives and bring about unique physical properties. Some interesting examples, such as intercalated polymer and silica network by topochemical polymerisation, fabrication of disk-like semiconductor nanocrystals and metal nanoparticles by hybrid perovskite templates are described.

Layered organic-inorganic hybrid perovskites: structure, optical properties, film preparation, patterning and templating engineering

Pulsed deuteron NMR spectroscopy is described, which has recently been developed to become a powerful tool for studying molecular dynamics in solid polymers. It is shown that by analyzing the line shapes of2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. By applying these techniques to selectively deuterated polymers, motional mechanisms involving different segments of the monomer unit can be monitored. In addition, motional heterogeneities in glassy polymers can be detected. The information about polymer dynamics available now is illustrated by a number of experimental examples. The chain motion in the amorphous regions of linearpolyethylene is discussed in detail and it is shown that it can clearly be distinguished from the chain motion of an amorphous polymer above the glass transition, wherepolystyrene is used as an example. Localized motions in the glassy state are illustrated through the jump motion phenyl groups exhibit both in the main chain (polycarbonate) and as a side group (polystyrene). The latter polymers also serve as examples for detecting motional heterogeneity. Finally, the mobility in novel classes of systems,liquid crystalline polymers andpolymer model membranes as revealed by2H NMR are described.

Molecular dynamics of solid polymers as revealed by deuteron NMR

The two structural phase transitions in the perovskite layer structure compound (C10H21NH3)2CdCl4 at Tc1=35 °C and Tc2=39 °C have been studied by x‐ray diffractional, calorimetric and dielectric measurements, proton NMR spin–lattice relaxation and second moment investigations, 35Cl and 14N quadrupole resonance spectroscopy as well as group theoretical considerations. The results show that the transition (Tc1) from the low temperature phase (P21/n) to the intermediate temperature phase (Pmnn) is basically a dynamic order–disorder transition of rigid alkyl chains, whereas the transition (Tc2) from the intermediate to the high temperature phase (Amaa) is connected with a melting of the alkyl chains. In the intermediate phase the rigid alkyl chains are flipping around their long axes between two equivalent orientations separated by 90°. The two transitions are somewhat analogous to the ones found in the lipid bilayer membranes and can be described by order parameters used for smectic liquid crystals.

Dynamics of the n‐decylammonium chains in the perovskite‐type layer structure compound (C10H21NH3)2CdCl4

The temperature dependences of the second moments M2 of the proton magnetic resonance absorption spectra and of the proton spin–lattice relaxation times T1 of perovskite layer compounds (CnH2n+1NH3)2CdCl4 with n=1–3 and (NH3– (CH2)n–NH3) CdCl4 with n=2−5 have been studied together with the frequency dispersion of T1. The structural phase transitions in these compounds were found to be connected with a change in the state of motion of the alkyl or alkylene groups, i.e., by an interplay of transitions between different N–H−−−Cl hydrogen bonding schemes and the excitation of hindered rotations of the hydrocarbon chains.

Proton NMR study of the structural phase transitions in perovskite layer compounds: (CnH2n+1NH3)2CdCl4 and (NH3–(CH2)n–NH3) CdCl4

Deuteron quadrupole coupling in KDF2

In this paper, we present a novel parallel dimension-independent node positioning algorithm that is capable of generating nodes with variable density, suitable for meshless numerical analysis. A very efficient sequential algorithm based on Poisson disc sampling is parallelized for use on shared-memory computers, such as the modern workstations with multi-core processors. The parallel algorithm uses a global spatial indexing method with its data divided into two levels, which allows for an efficient multi-threaded implementation. The addition of bootstrapping enables the algorithm to use any number of parallel threads while remaining as general as its sequential variant. We demonstrate the algorithm performance on six complex 2- and 3-dimensional domains, which are either of non rectangular shape or have varying nodal spacing or both. We perform a run-time analysis of the algorithm, to demonstrate its ability to reach high speedups regardless of the domain and to show how well it scales on the experimental hardware with 16 processor cores. We also analyse the algorithm in terms of the effects of domain shape, quality of point placement, and various parallelization overheads. 

Parallel domain discretization algorithm for RBF-FD and other meshless numerical methods for solving PDEs

The 31P chemical shift tensors σ have been determined above and below Tc. The spin–lattice relaxation time T1 (31P) was measured as a function of temperature at 109.3 and 36.4 MHz. The paraelectric 31P chemical shift tensor was found to be the average of the two tensors observed in the ferroelectric phase. This shows that the phase transition is triggered by the ordering of the O–H(2) ⋅⋅⋅O deuterons. The intrinsic O–H(2) ⋅⋅⋅O deuteron intrabond jump time is, in the absence of the interactions, of the same order as in KD2PO4. The anomalously short T1 (31P) is the result of an ’’anisotropy slowing down’’ of the order parameter fluctuations due to the pseudo‐one dimensional nature of correlations in CsD2PO4.

J. Slak

Papers

Dynamics of the n‐decylammonium chains in the perovskite‐type layer structure compound (C10H21NH3)2CdCl4

Proton NMR study of the structural phase transitions in perovskite layer compounds: (CnH2n+1NH3)2CdCl4 and (NH3–(CH2)n–NH3) CdCl4

Deuteron quadrupole coupling in KDF2

Parallel domain discretization algorithm for RBF-FD and other meshless numerical methods for solving PDEs

31P chemical shift and relaxation study of the pseudo‐one‐dimensional ferroelectric transition in CsD2PO4